Apparatus for compacting concrete



r o a 1 E. G. CARR APPARATUS FOR COMPACTING CONCRETE Filed 001:. 8.-1917 INVENTOR. Edward 7. arn

WITNESS:

425m zfm'lid A TTORNE YS.

Patented July 15, i924.

orrao srarss EDWARD G. CARR, OF OAKLAND, CALIFORNIA.

APPARATUS FOR COMPAGTI'NG concerns Application filed October To allwhom'z't may concern:

Be it known that I, EDWARD Gr. CARR,- a

' citizen ofthe United States, residing at Oakland, in the county ofAlameda and State of California, have invented new and usefulImprovements in Apparatus for Compacting Concrete, of which thefollowing is a specification.

This invention relates to the preparation of mixtures, such as concrete,for solidification, by compactly arranging the solid particles in themass, and-is especially applicableto the manufacturing of concreteroadin a practical manner to concrete roadways in Patent No. 1,203,482,issued to me October 81st, 1916, wherein an apparatus was rovided forspeeding up the successive b ows of the tamper, accomplishing more workin a given interval of time and to a greater degree improving thequality of that work. It did not, however, remove particles of air 1. bymeans of suction and became less elfectiveas the amount of free moisturein the,

mass wasu'educed.

The present invention lies in the process of and apparatus for employingsuction to compact a mass of concrete in plastic condition bywithdrawing a solid surface (which may or may not have been applied tothe concrete in a forcible manner) so quickly and suddenly as to createa suction or partial vacuum between that surface and the mass to becompacted. Such a suction creates a disturbance or agitation in themass, opposite in direction from that produced by pressure exertedthereupon, and a pressure within the mass acting in direction toward itssurface, this latter pressure acting to force the moisture out of theconcrete, to cause air particles to expand and burst their way out tothe surface, and to agitate its component particles. In other words, by

a; 1917. Serial No. 195,473.

this invention moisture is sucked and air caused to blow itself out ofthe mass, where- .as prior hereto the method has been to squeeze themout if at all.

When a thrust pressure is applied alternately with suction, agitationwithin the mass in two relatively opposite directions is produced whichcauses the individual solid particles in the concrete to shift withrelation toeach other, whereas the most enlightened method heretoforeknown has been merely to agitate the mass as a whole, if at all, and inone direction only. Since the movement, due to suction, tends to agitatethe mass and its particles in a direction opposite to that of a struck'blow thereon, when this suction is introduced between the strikin .ofblows upon the mass, the rock or other solid particles are preventedfrom jamming across one another and are caused to be arranged morecompactly. Rocks will jam just like logs and a steady or intermittentpressure or pounding of the mass in the same direction will not disengae them to any appreciable extent. But w en, being jammed, the particlesin the mass are agitated by a force acting in a direction opposite tothat of an imposed pressure upon the mass the keystone of the rockswhich have jammed into an arch, as it were, will be upset and the rockswill tumble into closer union,

In addition to this agitation, thecreation of a vacuum permits the airparticles in the mass, which are under atmospheric or greater pressure,to exercise relatively greater force against the containing walls ofsolid matter and thus literally to explode their way to the surface. Ina so-called dry mixture there has heretofore been no effective method ofremoving this air.

Referring now to the drawings:

Fig. 1 is a side elevation of the apparatus by which the method ofcompacting concrete is practiced.

Fig. 2' is a plan view of the apparatus shown in Fig. 1.

Fig. 3 is a cross section of the vacuum-producing member of saidapparatus at the commencement of its upward or vacuumproducing stroke.

Fig, 4; is a cross section of the vacuumproducing member of saidapparatus at the conclusion of its upward or vacuum-producing stroke.

The apparatus used by me in practicing the bar 6 to move downwardl thisprocess, which is particularly designed for its use in the manufactureof highways, is in its source of power, means of locomotion and framesimilar to the device disclosed in United States Letters Patent No.1,204,2i5, heretofore granted to me. But whereas in that patent, meansis disclosed for applying a varying or intermittent pressure upon thesurface of the concrete through a tamping bar flexibly connected to theframe and held at the said surface there is no suction produced orprovided for.

In the structure now disclosed there is a bar 6 which is shod with achannel iron 7 to keep the corners thereof from wearing and destroyingthe vacuum-producing surface.

Said bar 6 is suspended at either end across the surface to be compactedby laminated springs 2 which hold the bar 6 an appreciable distanceabove the level of the surface 10 to be compacted, in the device shownthis distance being at least two inches.

These springs 2 are fastened to the frame 11 at one end by a bracket 12and at the other end by a shackle 13. Power is supplied from a motor at14 and conveyed to a shaft 15 which actuates the wheels 16 of the framethrough the wheels 17 and a belt 18, causing it to travel. Power is alsotransmitted to shafts 19-19 and thence through a universal joint 20 toan unbalanced weight 21.

The tendency of the weight 21 to rotate out of its center of; mass bycentrifugal force causes shaft 19" to have an up and down movement. Thismovement causes against the springs 2 and thrust against t e surface tobe compacted. It will force its way a slight distance'into the mass, asshown in Fig. 3. The springs 2 are distorted downwardly so that at theinstant the downward-stroke is completed the bar 6 is quickly jerkedback up to the level of the bar when at rest and several inches abovethe surface to be compacted. This sudden lift creates a partial vacuumor suction which causes 2 the bubbles of air in the mass to expand andblow out, the particles of rock to shift with relation to each other andbreak up any ex isting jams, and sucks out the moisture.

The frame is, during the operation, slowly moved along the highway, theconcrete of which is to be compacted, through the motion of the wheels16 at a speed of travel very much less for the interval of time employedin one vacuum production than isthe width of the bar 6, so that thesuccessive areas covered by the bar 6 overlap, thereby ensuring a smoothsurface and thorough and even compacting.

While the benefits of the invention are secured irrespective of thespeed at which the successive strokes and sudden lifts take place, thebest results are obtainable if each individual mo ement of alternatestrokes and uplift com s before the agitation, produced in the mass bythe preceding movement, has ceased. Rapid applications of pressure,so-called vibrations, were heretofore employed by me as a means ofagitating a mass of concrete as a whole, butthe agitation was therebyproduced by a pressure or thrust in one direction only and thereforecalled for down strokes of the bar 6 just twice as rapid as arenecessary in my new process and apparatus, since the new one produces aforce in two directions for each cycle from one down stroke to anotherand thus produces twice as many agitations for the same speed ofoperation.

Other advantages are that by this process the proportion of rock in theconcrete can be greatly increased, with a corresponding saving of cementor other binding means, which is the expensive element, this beingoccasioned by the greater compacting of the rock; a mixture can becompacted by this method which is drier than a mixture which can betamped, s that there is less water to be removed and less possibleporosity; and a concrete of superior hardness and solidity is formed,since the air is removed therefrom and in addition moisture, both ofwhich, when the concrete has solidified, tend to make itporous and todisintegrate.

The word suction is used in this specification and in the claim in itsordinary. and commonly accepted significance. Looking at Fig. 4 of thedrawings, the concrete which is shown lifted up is, of course, elevatedby the pressure of the air on the adjacent surfaces of the concrete.When the bar 6 is raised suddenly or quickly, when in contact with theconcrete, the air pressure on the top of the concrete adjacent the baris exerted through the mass of the concrete to fill the vacuum createdby the bar in its ascent. The air is pressing upon the con-' crete witha force of about fifteen pounds per square inch. Taking into account ona road fourteen feet wide a strip across the road adjacent one side ofthe bar and extending only one inch in the length of the road, the airpressure exerted upon this strip will be over a ton and a quarter,figuring the pressure at fifteen pounds per square inch.

The pressure exerted by the air is that of a fluid under pressure andthe pressure is transmitted through the plastic part of the come, apartfrom inertia, and any bridges or arches which these pieces of crushedrock have formed are destroyed. The plastic part of the concrete movesand rises and falls in the same manner as liquid and plastic masses andits effect in producing motion of the pieces of crushed rock bodilydepends upon the viscosity of the plastic mass, its velocity of movementand the cross-sectional areas of the pieces of rock in the direction offlow. But for all practical purposes in connection with this invention,the real advantage is the upward movementof the plastic mass between thecrushed rock and the re-settling of the crushed rock. A downwardpressure upon a mass of concrete, when the plastic part of the concretecan be displaced, usually results in forming bridges or arches withpieces of the rockwhich prevent further compacting. By moving theconcrete mass up and down a shakin of the mass is produced which results1n a more complete and closer assemblage of the pieces of crushed rockwhich are ordinarily used to constitute part'of the concrete mass. Thesand used in concrete is not ordinarily graded to a uniform size and theup and down movement of the concrete mass tends to move the sandparticles and sift the smaller pieces into spaces which are too smallfor the largerpieces.

The springs 2 are means for giving a essary being that the bar 6 begiven a quick,

powerful lift so that the pressure of the air adjacent the bar will liftthe concrete under the bar.

Having thus described "my invention, what I claim and desire to secureby Letters Patent is An apparatus for tamping concrete roadways in thecourse of manufacture, comprising a carriage, a vertically reciprocatingtamping bar carried thereby, laminated springs for suspending saidtamping bar from the carriage, and means for moving the tamping bardownwardly into engagement with the surface of the concrete mass, saidsprings acting to lift the tamping bar with such suddenness as to causea suction to be applied thereby to the surface of the mass.

In testimony whereof I have hereunto set my hand in the presence of twosubscribing witnesses.

EDWARD G. CARR.

Witnesses:

M. E. DOWNEY, THOMAS P. Bnrr'r.

